how to swap fn and ctrl keys

I've got a new Precision 5520 running Ubuntu 16.04. After at least ten years using a MacBook Pro, my left hand demands that the Ctrl and Fn keys be swapped. I understand the Fn key is handled at the lowest level. Poking around in the BIOS, I could find no way to swap them at that level. Is there a way to accomplish this seemingly simple feat, perhaps using xmodmap (which I've not investigated yet, as it seems to be too high level)?

(Apologies for using the Alienware Forum place. That seems to be the only valid Location, and the forum software required me to fill it in.)